File management and Performance

1

• File management and Performance

2

• File Systems Architecture

• File organization and access
• sequential
• index-sequential
• direct

3

• File sharing and blocking

• File sharing
• access rights read, write, execute, by user
  classes.
• File/record locking simultaneous access
• Record blocking
• Logical vs physical record
• unblocked vs blocked record
• fixed-lenght vs variable-lenght

4

• File allocation

• File allocation table (FAT)
• Pre allocation vs dynamic allocation
• Portion size
• contiguity increases performance
• fixed-size portions simplify reallocation
• variable-size or small fixed-size minimizes waste
  of unused space for overallocation
• two main alternatives
• variable, large contiguous portions (performance)
• small fixed portions (flexibility)
• File fragmentation and reorganization

5
Redundant Array of Independent/ Inexpensive
Disks (RAID)

• RAID is a set of physical disk drives viewed by
  the OS as a single logical drive
• Data are distributed across the physical drives
  of an array
• Redundant disk capacity is used to store parity
  information, which guarantees data recovery
• RAID Levels various levels of performance and
  redundancy
• the disks are divided in strips physical blocks,
  sectors, or similar
• the strips are mapped round robin on the array
• I/O requests can be processed in parallel

6

• Performance

• How effective is the OS in managing resources?
• Overall performance measures
• turnaround time
• response time
• throughput
• workload
• capacity
• utilization
• Bottlenecks

7

• Evaluation Techniques

• Timings (hardware)
• Instruction mix (software mix)
• Kernel (typical program)
• Benchmarks (comparison between systems)
• Synthetic programs
• Analytical models and simulation
• Commercial performance packages

8

• Performance enhancement

• coprocessing
• parallel processing
• the RISC vs CISC controversy
• CISC
• frequently used code as (complex) instructions
• increase lower level programming productivity
• extensive market penetration
• RISC
• very few of the complex instructions are used
  (empirical studies)
• therefore a reduced instruction set is more
  efficient
• programs are 20 larger , requiring more disk
  space and memory
• much more registers are needed, but speed of
  programs written for RISC is close to twice of
  equivalent for CISC.
• facilitate scalability